Breast cancer is responsible for the second overall cause of cancer-related deaths among women. Currently, prevention of breast cancer predominantly involves reducing modifiable risks including early detection through physical examination and mammograms, avoidance of unnecessary post-menopausal hormone therapy, reduction in alcohol consumption, loss of weight, increase in physical activity, and genetic testing for mutations of the breast cancer type 1 and type 2 susceptibility genes (BRCA1 and BRCA2, respectively). More aggressive approaches in high risk patients include chemoprevention with tamoxifen, raloxifene, and aromatase inhibitors as well as prophylactic bilateral mastectomy and oophorectomy.
Despite the profound health risk of breast cancer and inadequacy of preventative efforts, an immunotherapy for breast cancer has not been developed as an integral part of the standard of care. Tumor-specific antigens have long provided less than optimal results as targets for cancer vaccination. The overall goal of cancer vaccination has traditionally been to boost the latent immune response to tumor-specific antigens. Approaches have included cell-based protocols involving immunization with whole autologous or allogeneic tumors, as well as antigen-based strategies involving immunization with proteins or peptides overexpressed in tumors and underexpressed in normal tissues. The human epidermal growth factor receptor 2 (HER2) and mucin (MUC1) are the predominant antigens used in human breast cancer vaccine trials. Although vaccination using these antigens may demonstrate tumor reducing effects, neither antigen provides any tissue or tumor specificity since both are expressed in a variety of normal tissues and tumors. Thus, the lack of inherent tissue specificity of HER2 and MUC1 targeted immunity may ultimately lead to substantial systemic autoimmune sequelae if a robust immune response manifests.
A full-strength autoimmune attack sufficient to induce targeted breast failure can provide effective therapy against established breast malignancies if the target antigen is constitutively expressed in breast tumors. Moreover, if the selected target antigen is expressed in normal breast tissue under conditions that are easily avoidable, then the vaccine may provide safe and effective protection against the development of breast cancer.
Human alpha-lactalbumin (α-lactalbumin) is a conditionally expressed, breast specific differentiation protein found in the majority of breast malignancies. As an integral differentiation protein involved in regulation of lactose biosynthesis, expression of α-lactalbumin is breast-specific and conditionally dependent on lactation for its expression and synthesis. Human α-lactalbumin is also constitutively overexpressed in the majority of breast tumors, is breast specific, and is sufficiently immunogenic to induce an effective proinflammatory immune response. Thus, immunization against human α-lactalbumin offers a safe and effective vaccination strategy for the prevention of breast cancer.
Our extensive studies using α-lactalbumin immunization in murine tumor models demonstrate its significant potential in inhibiting breast tumor growth especially when administered in a prophylactic setting or early during breast tumor growth. Based on these studies with α-lactalbumin applicants have established a set of principles for selection of immunotherapeutic targets for vaccination and prevention of breast cancer, namely 1) the antigen must be constitutively overexpressed in the majority of targeted tumors; 2) expression of the target antigen in normal tissue must be conditional; and 3) the condition determining expression of the target antigen in normal tissue must be readily avoidable. Under these prerequisites, lactation proteins, that are characterized by expression restricted to and dependent on the functional condition of the breast stand out as ideal candidate targets for preventive breast cancer vaccination.
Based on the significant anti-tumor response achieved by α-lactalbumin vaccination in the absence of collateral inflammation to normal tissues, applicants conclude that a multivalent vaccine comprised of two or more candidate lactation proteins would substantially enhance the efficacy of vaccination against breast tumors. The enhancement in anti-tumor effect by using a multivalent vaccination approach would be achieved on two levels: 1) by increasing the strength of immune response against arising tumor due to activation of a larger T cell repertoire comprised of multiple T cell lineages reactive to more than one tumor specific target; 2) by covering a broader range of tumors, including those that do not express the protein targeted by a univalent vaccination approach such as α-lactalbumin. In addition, a multivalent vaccine will have the potential to target tumors that have lost or down-regulated expression of one or more proteins or acquired expression of alternate proteins due to transcriptional dysregulation during their evolution from normal to dysplastic, to carcinoma in situ, to invasive, and to metastatic stages of breast tumor evolution. In other words, a multivalent vaccine approach will apply greater multi-target immunological pressure both on early and evolving tumors. It will thereby cover a larger tumor variety and increase efficacy of prevention as well as provide more effective therapy by lowering the probability of tumor escape and generation of resistance to the vaccine.